In dealing with the sexual instinct the first two factors are those which we have most fully to discuss.  With the external stimuli we shall be concerned in a future volume (iv).  We may here confine ourselves mainly to the first factor:  the nature of the internal messages which prompt the sexual act.  We may, in other words, attempt to analyze the sexual impulse.

The first definition of the sexual impulse we meet with is that which regards it as an impulse of evacuation.  The psychological element is thus reduced to a minimum.  It is true that, especially in early life, the emotions caused by forced repression of the excretions are frequently massive or acute in the highest degree, and the joy of relief correspondingly great.  But in adult life, on most occasions, these desires can be largely pushed into the background of consciousness, partly by training, partly by the fact that involuntary muscular activity is less imperative in adult life; so that the ideal element in connection with the ordinary excretions is almost a negligible quantity.  The evacuation theory of the sexual instinct is, however, that which has most popular vogue, and the cynic delights to express it in crude language.  It is the view that appeals to the criminal mind, and in the slang of French criminals the brothel is le cloaque.  It was also the view implicitly accepted by medieval ascetic writers, who regarded woman as “a temple built over a sewer,” and from a very different standpoint it was concisely set forth by Montaigne, who has doubtless contributed greatly to support this view of the matter:  “I find,” he said, “that Venus, after all, is nothing more than the pleasure of discharging our vessels, just as nature renders pleasurable the discharges from other parts."[2] Luther, again, always compared the sexual to the excretory impulse, and said that marriage was just as necessary as the emission of urine.  Sir Thomas More, also, in the second book of Utopia, referring to the pleasure of evacuation, speaks of that felt “when we do our natural easement, or when we be doing the act of generation.”  This view would, however, scarcely deserve serious consideration if various distinguished investigators, among whom Fere may be specially mentioned, had not accepted it as the best and most accurate definition of the sexual impulse.  “The genesic need may be considered,” writes Fere, “as a need of evacuation; the choice is determined by the excitations which render the evacuation more agreeable."[3] Certain facts observed in the lower animals tend to support this view; it is, therefore, necessary, in the first place, to set forth the main results of observation on this matter.  Spallanzani had shown how the male frog during coitus will undergo the most horrible mutilations, even decapitation, and yet resolutely continue the act of intercourse, which lasts from four to ten days, sitting on the back of the female and firmly clasping her with his forelegs.  Goltz